1: The computer cannot be denser than that which would create a black hole (Bekenstein bound)
2: The temperature of the cosmic microwave background radiation sets the minimum operating temperature
3: Heisenberg’s Uncertainty Principle, Planck’s constant,E = mc2 set a maximum on the energy processing per unit mass (2 x 1047 bits per second per gram of its mass)
4: Due to the second law of thermodynamics, there is a minimum to the energy consumption per computation (Landauer limit)
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